Resolve "Make testing data files cwd invariant"

Makefile

src/tests/test_analysis/test_cavity/test_finesse.py

src/tests/test_analysis/test_cavity/test_linewidth.py

src/tests/test_analysis/test_cavity/test_modematching.py

...ests/test_analysis/test_servo_design/test_servo_design.py

src/tests/test_conversion/test_db/test_db.py

src/tests/test_gaussian_beam/test_fit_beam_data.py

src/tests/test_io/test___init__/test_read.py

src/tests/test_io/test___init__/test_reads.py

src/tests/test_io/test_data_container/test_data_container.py

..._io/test_importers/test_ascii_header/test_ascii_header.py

...orters/test_data_container_csv/test_data_container_csv.py

...sts/test_io/test_importers/test_gwinstek/test_gwinstek.py

..._io/test_importers/test_gwinstek_LSF/test_gwinstek_LSF.py

...tests/test_io/test_importers/test_hp4395a/test_hp4395a.py

...st_importers/test_keysight_binary/test_keysight_binary.py

..._io/test_importers/test_keysight_csv/test_keysight_csv.py

..._io/test_importers/test_keysight_fra/test_keysight_fra.py

...o/test_importers/test_rhode_schwarz/test_rhode_schwarz.py

...s/test_io/test_importers/test_tektronix/test_tektronix.py